1. Field of the Invention
The present invention relates to a position sensor, a method for detecting a position, an alignment apparatus including the position sensor, and a method for alignment.
2. Description of the Related Art
Contact exposure apparatuses, in which a mask pattern is brought into intimate contact with a resist on a wafer and exposure and transfer are performed, are previously known as exposure apparatuses for fabricating high-density semiconductor integrated circuits and the like.
A contact exposure apparatus that uses evanescent light is proposed as one such exposure apparatus in, for example, U.S. Pat. No. 6,171,730. The invention described in U.S. Pat. No. 6,171,730 is excellent, and makes a significant contribution to the areas of photolithography and semiconductor manufacturing technology. The exposure apparatus described in U.S. Pat. No. 6,171,730 is shown in FIG. 14.
In the apparatus shown in FIG. 14, a resist film 107 is formed on the surface of a substrate (wafer) 106 so as to prepare an object to be exposed. The substrate is attached on stage 108 and the stage 108 is driven to align the substrate 106 relative to a photomask 101. The stage 108 is driven in a direction normal to the mask surface to bring the photomask 101 into intimate contact with the resist 107 on the substrate 106, and the resist 107 is exposed to evanescent light generated in the vicinity of fine apertures on the front of the photomask 101, by the use of exposure light 110 emitted from an exposure light source 109.
With respect to the alignment between the above-described photomask and the substrate in such a contact exposure apparatus, only the alignment of the substrate (wafer) relative to the photomask has been previously performed in the two-dimensional direction on the mask surface, that is, only horizontal alignment is performed, and performing alignment through the use of a microscope observation is conventional.
However, in known contact exposure apparatuses, no device for measuring and controlling the distance between a mask and a wafer is provided, and only horizontal alignment is performed to align the mask with the wafer, as described above. Consequently, the measurement and the control of the distance between a mask and a wafer required in the case of, for example, exposure to the evanescent light by the use of an intimately contacted mask cannot be performed.
With respect to the horizontal alignment through the use of a microscope observation in a known contact exposure apparatus, the accuracy of the alignment may be on the order of 1 μm, and may not be comparable to the accuracy (100 nm or better) required of an evanescent-light exposure apparatus, for example.
If the construction of the device for measuring and controlling the distance between a mask and a wafer is attempted by the use of, for example, known distance-measuring technology, e.g., laser telemetry, the configuration of the apparatus becomes complicated significantly.